The present invention relates to hydroprocessing of heavy hydrocarbonaceous materials. More particularly, the invention involves the hydroprocessing of hydrocarbonaceous liquids containing n-heptane-insoluble asphaltenes.
The presence of n-heptane-insoluble asphaltenes in heavy oils such as coal derived oils, shale oil, oil derived from tar sands, and heavy petroleum or petroleum fractions has long been recognized as a complication in hydroprocessing. The large effective diameter of asphaltene molecules, typically 100 to 600 Angstroms, does not permit their entry into the pores of many commercial hydroprocessing catalysts. Conversion of asphaltenes during catalytic hydroprocessing has therefore required the development of special large-pore catalysts. Such catalysts, however, tend to have lower surface areas than conventional hydroprocessing catalysts and therefore tend to be less active. As a result many commercial hydroprocessing units have not been effective for totally converting asphaltenes. The presence of asphaltenes is particularly bothersome in feedstocks containing significant amounts of solids, such as liquids derived from coal, oil shale, tar sands, gilsonite or other solid carbonaceous materials.
Various techniques have been employed for the removal of asphaltenes from heavy hydrocarbons including solvent deasphalting and catalytic hydrogenative deasphalting. Other approaches have focused upon suppressing the formation of asphaltenes. See, for example, U.S. Pat. No. 4,081,360, issued Mar. 28, 1978 to Tan et al where light solvents are added to coal liquefaction fractions.